What is a preprint server?

Preprint servers are freely accessible online digital archives for early drafts of research outputs, submitted by the authors (known as self-archiving). Preprint servers may be subject-specific, others accept submissions covering all areas of research. By posting to preprint servers, authors are able to make their findings available to the scientific community and receive feedback on draft manuscripts before they are submitted to journals. arXiv, bioRxiv, are examples of preprint servers.